stabilization of black cotton soil

CHAPTER 1

INTRODUCTION 1.1

SOIL STABILIZATION

1.1.1 General The strength and life of any structure depends on its foundation. For that reason, soil is a critical element influencing the success of any construction project. Soil is an important part of the foundation and any construction process. Therefore, understanding the engineering properties of soil is crucial to obtain strength and economic permanence. Soil stabilization is the process of maximizing the suitability of soil for a given construction purpose. Soil is the basic construction material. It supports the substructure of any structure and it is the subgrade which supports the sub base/base in the pavement. The existing soil at a particular location may not be suitable for the construction due to poor bearing capacity and higher compressibility or even sometimes excessive swelling in case of expansive soils. The improvement of soil at a site is indispensible due to rising cost of the land, and there is huge demand for high rise buildings. There is a need to concentrate on improving properties of soils using cost effective practices. Soil stabilization means the improvement of stability or bearing power of the soil by the use of controlled compaction or the addition of suitable admixture or stabilisers. Unstable soil creates variety of problems ranging in severity from workable soil to dangerous and unattractive muddy soil.

1.1.2 Brief History The necessity of improving the engineering properties of soil has been recognized for as long as construction has existed. Many ancient cultures, including the Chinese, Romans, and Incas, utilized various techniques to improve soil stability, some of which were so effective that many of the buildings and roadways they constructed still exist today. In the United States, the modern era of soil stabilization began during the1960s and ‟70s, when general shortages of aggregates and petroleum resources forced engineers Department of Civil Engineering, MIT Mysore

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to consider alternatives to the conventional technique of replacing poor soils at building sites and stabilize the weak soils. This time, however, soil stabilization is benefiting from better research, materials and equipment.

1.1.3 Definition of Soil Stabilization In general soil stabilization consists of two elements; increase the stiffness of Soil and maintain stiffness by maintaining correct moisture content. This practice can be used to lower the compressibility of soil and therefore reduce the settlement when structures building on it. The term soil stabilization means the improvement of the stability or bearing Power of the soil by controlled compaction or by the addition of suitable admixtures and stabilizers. Soil stabilization deals with Physio-chemical and Chemical Methods to make the stabilized soil serve its purpose as pavement component material. Soil Stabilization is the alteration of soils to enhance their physical properties. Stabilization can increase the shear strength of a soil and/or control the shrinkswell properties of a soil, thus improving the load bearing capacity of a sub grade to support pavements and foundations. Stabilization can be used to treat a wide range of sub grade materials, varying from expansive clays to granular materi als. This process is accomplished using a wide variety of additives, including lime, fly-ash, and Portland cement. Other materials by products used in stabilization include lime-kiln dust and cement-kiln dust. Proper design and testing is an important component of any stabilization project. This testing will establish proper design criteria in determining the proper additive and admixture rate to be used to achieve the desired engineering properties.

1.1.4 Why It Is Used? Traditionally, stable sub-grades, sub-bases and/or bases have been constructed by using selected, well-graded aggregates, making it fairly easy to predict the load-bearing capacity of the constructed layers. By using select material, the engineer knows that the foundation will be able to support the design loading. Gradation is an important soil characteristic to understand. A soil is considered either “well“well-graded” or “uniformly“uniformly-graded” (also referred to as “poorly“poorly-graded”). This is a reference to the sizes of the particles in the materials. Uniformly-graded materials are made up of individual particles of roughly the same size. Well-graded materials are made up of an optimal range of different sized Department of Civil Engineering, MIT Mysore

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particles. It is desirable from an engineering standpoint to build upon a foundation of ideal and consistent density. Thus, the goal of soil stabili zation is to provide a solid, stable foundation. “Density” is the measure of weight by volume by volume of a material, and is one of the relied-upon measures of the suitability of a material for construction purposes. The more density a material possesses, the fewer voids are present. Voids are the enemy of road construction; voids provide a place for moisture to go, and make the material less stable by allowing it to shift under changing pressure, temperature and moisture conditions. Uniformly-graded materials, because of their uniform size, are much less dense than well-graded materials. The high proportion of voids per volume of uniformly-graded material makes it unsuitable for construction purposes. In well-graded materials, smaller particles pack into the voids between the larger particles, enabling the material to achieve high degrees of density. Therefore, well-graded materials offer higher stability, and are in high demand for construction . With the increased global demand for energy and increasing local demand for aggregates, it has become expensive from a material cost and energy use standpoint to remove inferior soils and replace them with choice, well-graded aggregates. One way to reduce the amount of select material needed for base construction is to improve the existing soil enough to provide strength and conform to engineering standards. This is where soil stabilization has become a cost-effective alternative. Essentially, soil stabilization allows engineers to distribute a larger load with less material over a longer life cycle. There are many advantages to soil stabilization: 1. Stabilized soil functions as a working platform for the project 2. Stabilization waterproofs the soil 3. Stabilization improves soil strength 4. Stabilization helps reduce soil volume change due to temperature or moisture 5. Stabilization improves soil workability 6. Stabilization reduces dust in work environment 7. Stabilization upgrades marginal materials 8. Stabilization improves durability 9. Stabilization dries wet soils 10. Stabilization conserves aggregate materials 11. Stabilization reduces cost 12. Stabilization conserves energy Department of Civil Engineering, MIT Mysore

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1.1.5 Principle of Soil Stabilization The basic principles in soil stabilization are as follows: 

Evaluating the properties of given soil.

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Deciding the method of supplementing the lacking property by the effective and economical method of stabilization.

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Designing the stabilized soil mix for intended stabilit y and durability values.

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Considering the construction procedure by adequately compacting the Stabilized layers.

1.1.6 Applications of Soil Stabilization Soil Stabilization can be used in a number of different applications ranging from new pavements, to environmental remediation. It is used in many sectors of the construction industry. Roads, parking lots, airport runways, building sites, landfills, and soil remediation all use some form of soil stabilization. Other applications include waterway management, mining, and agriculture. Following are the few applications; 1. Foundations and Structural Support

There are three basic soil conditions that pose particularity serious problems for architects, engineers and building contractors. First is the swelling and shrinkage movements of expansive clays; secondly, the occurrences of settlement or densification from load bearing forces; and, thirdly, the influence of moisture on the soil and building structure. Individually any one of these soil behaviors would create tremendous economic damage to a building structure. The chemical stabilization process addresses these three basic soil concerns in several meaningful ways including: reduction of shrink/swell potential and plasticity on expansive clays, increased load bearing support as measured by unconfined compressive strength, and reduction of the treated soils permeability, making it less susceptible to water infiltration. Expansive Soils

Expansive clay soils undergo large amounts of heaving and shrinking due to seasonal moisture changes. These movements lead to cracking and buckling of the infrastructure built on the expansive soils and can result in billions of dollars of damage annually. To mitigate the effects of expansive soils Geotechnical engineers have had the option to remove expansive materials from structural areas and replace them with non-expansive imported material or mechanically stabilize the expansive clay by over-optimizing the moisture during compaction. Department of Civil Engineering, MIT Mysore

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Both of these methods have inherent limitations-the practice of export/import has become cost prohibitive in today's economy, while environmentally it's disruptive to the surrounding communities and exhausts the minimal resources that are available. Mechanically stabilizing the expansive clay by over-optimizing the moisture content leads to issues of lower compaction and does little to reduce the continual fluctuation of moisture content in the future. Load Bearing Strength

The depletion and cost of quality construction materials for engineering applications continually confronts material engineers and designers. Even if good quality construction materials are available, the cost and environmental impact of transporting these materials have begun to preclude their use. To address these economic and environmental realities, designers and engineers have turned to chemical stabilization as a method to increase the bearing capacity of native soils used both in shallow and deep foundation support. Chemical treatment of non-cohesive or unstable soils with a cementitious stabilizer creates engineering benefits that result in increased bearing strength and durability. Dependent on soil type and percent of stabilizer, strength gains can develop above 1,000 psi, although most foundation support applications would only require unconfined compressive strength of less than 300 psi. Stabilized Section as Moisture Barrier

To achieve low permeability, the voids and pore spaces in a material should be minimized or filled. Compacted clay has a low permeability, but lacks the other desirable properties of a suitable structural section - compressive strength and durability. Chemical soil stabilization

brings

improved

strength

and

durability

without

sacrificing

the

impermeability associated with clays.

2. New Pavements

Pavements, especially flexible pavements, are constantly under changing conditions, thus they are inherently unstable. Water infiltration weakens the underlying soil condition and variable loading moves those conditions throughout the pavement structure. Asphaltic concrete pavements are constantly under the debilitating effects of oxidation and the actions of water stripping the asphaltic binder from the aggregate structure. The use of chemical stabilization in roadway design speaks directly to these issues of long-term lifecycle stability. Department of Civil Engineering, MIT Mysore

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Engineers are frequently required to incorporate poor quality soil and aggregate into pavement designs. These poor quality materials typically have the potential to demonstrate undesirable engineering behavior such as low bearing capacity, high shrink/swell potential, and poor wet-dry durability. Thus, engineers frequently seek to improve the engineering properties of poor quality soils and aggregates through chemical stabilization. Stabilization of various pavement sections can be in the form of in-situ subgrade improvements, stabilization of lesser quality subbase materials, or treatment of aggregate base material in the form of cement treated base. The criteria for establishing the engineering properties of soils used for pavement base courses, subbase courses, and subgrades by the use of chemical additives are applicable to all pavement types, including parking lots, low and high volume roads, and airfields.

3. Bio-Solid Processing Pads

The processing and removal of biosolids from waste management and composting facilities has traditionally been a major operational concern. Most large processing centers require removal of compost or sludge by large heavy equipment. This heavy loading creates a high fatigue factor on the native subgrade soils, causing the processing table to become weak and unstable under repetitive loading. Soil stabilization increases the load bearing strength, while reducing the permeability of the native soil.

4. Environmental Remediation

Soil Stabilization/Solidification (S/S) of soils contaminated with hazardous waste is a tried and proven chemical remediation technology. Both the technology and its acceptance has progressed dramatically over a number of years as a simple, cost effective and flexible treatment method for remediation of soils and recycling them back to usable land applications. Numerous contaminated sites operated by both government and private industry have been returned back to usable land with the in-situ chemical stabilization methods. Successful clean-up projects have been completed in the areas of soils contaminated with metal wastes, chemical wastes, and contaminated dredging.

5. Site Winterization

Construction sites are susceptible to rain delays that cost both time and money. When Department of Civil Engineering, MIT Mysore

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winter hits, project managers turn to the only proven method for site winterization, the process of chemically treating the surface soils to provide a high-strength and low permeable cementitious barrier. This type of treatment ensures immediate access to construction sites after a storm event, while eliminating fatigue rutting from repetitive loading.

6. Water Resources

The use of chemical stabilization in Water Resource projects has increased considerably. Factors that must be considered for chemical soil stabilization include cost of stabilizer, degree of suitable soil, special processing requirements, haul distance, dimensions and configuration of the slope protection and mixing and placement methods. For riprap, considerations include cost and availability of rock, size, haul distance, special processing requirements, configuration of placement and placement effort.

7. Other Applications

From an engineering standpoint, the chemical stabilization process addresses three basic soil concerns that are meaningful to engineers and designers, including; first, it reduces the shrink/swell potential and plasticity of expansive clays required for structural stability, secondly, treatment stabilizes the potential occurrences of settlement or densification from load bearing forces such as those imposed on pavements and other structures, by increasing the soil matrix unconfined compressive strength and thirdly it reduces the influence of moisture on the soil structure and reduces the soil's permeability for use in applications such as water resource liners and abutments. From an economic standpoint, chemical stabilization reduces a project's initial cost and to a greater extent its lifecycle cost. When comparing other stabilization alternatives, such as off hauling unsuitable materials and importing quarry products, the up-front construction saving may exceed 50 percent. Additional cost saving may be realized in schedule adherence, since the stabilized section develops and maintains a high strength low permeable mat structure that allows for all weather project access during the winter rainy months. In regards to environmental remediation applications, the stabilization process allows for contaminated soil to be encapsulated in-place or stabilized to a criteria that allows for conventional handling or off hauling.

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1.1.7 Types of Soil Stabilization 1. Mechanical Stabilization 2. Chemical Stabilization

Mechanical Stabilization Mechanical soil stabilization refers to either compaction or the introduction of fibrous and other non-biodegradable reinforcement to the soil. This practice does not require chemical change of the soil, although it is common to use both mechanical and chemical means to achieve specified stabilization. There are several methods used to achieve mechanical stabilization. Mechanical stabilization, or compaction, is the densification of soil by application of mechanical energy. Compaction is done at or near optimum moisture content. Densification occurs as air is expelled from soil voids without much change in water content. This method is particularly effective for cohesion less soils where compaction energy can cause particle rearrangement and particle interlocking. But, the technique may not be effective if these soils are subjected to significant moisture fluctuations. The efficiency of compaction may also diminish with an increase of the fine content, fraction smaller than about 75 microns, of the soil. This is because cohesion and inter particle bonding interferes with particle rearrangement during compaction. Mechanical stabilization is the process of improving the properties of the soil by changing the gradation. Mechanical stabilization is also known as granular stabilization. As the soil available at site may seldom meet both the gradation and the plasticity characteristics, it usually becomes necessary to mix soils from different sources to obtain desired mixture. Maximum use of locally available soils should be made for economy. It is generally used to improve the sub-grade of low bearing capacity and also for base and sub base construction. It is the simplest method of soil stabilization. The mechanical stability of the mixed soil depends on the degree of compaction, gradation, plasticity characteristics and compaction. Soils with sodium sulphates and sodium carbonates should not be used as they cause large volume changes due to hydration and dehydration. Gradation depends on type of layer which is going to be constructed. The mixture should contain a fair portion of different size particles. Mechanical stability depends on the degree of compaction. Compaction is to be done at or near the optimum moisture content. Department of Civil Engineering, MIT Mysore

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Chemical Stabilization One method of improving the engineering properties of soil is by adding chemicals or other materials to improve the existing soil. This technique is generally cost effective: for example, the cost, transportation, and processing of a stabilizing agent or additive such as soil cement or lime to treat an in-place soil material will probably be more economical than importing aggregate for the same thickness of base course. Chemical stabilization is achieved by the addition of proper percentages of cement, lime, fly ash, bitumen, polymers of these materials to the soil. The selection of type and determination of the percentage of additive to be used is dependent upon the soil classification and the degree of improvement in soil quality desired. Generally, smaller amounts of additives are required when it is simply desired to modify soil properties such as gradation, workability, and plasticity. When it is desired to improve the strength and durability significantly, larger quantities of additive are used. After the additive has been mixed with the soil, spreading and compaction are achieved by conventional means. Additives can be mechanical, meaning that upon addition to the parent soil their own load bearing properties bolster the engineering characteristics of the parent soil. Additives can also be chemical, meaning that the additive reacts with or changes the chemical properties of the soil, thereby upgrading its engineering properties. Placing the wrong kind or wrong amount of additive – or, improperly incorporating the additive into the soil – can have devastating results on the success of the project. So, in order to properly implement this technique, an engineer must have: 

A clear idea of the desired result

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An understanding of the type(s) of soil and their characteristic on site

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An understanding of the use of the additive(s), how they react with the soil type and other additives, and how they interact with the surrounding environment

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An understanding of and means of incorporating (mixing) the additive

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An understanding of how the resulting engineered soil will perform Combining the additives with the soil is typically done with various machines.

The method used is usually based on three factors: what machines are available, the location (urban or rural), and the additives that are being used. The mixing should be as uniform as possible.


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1.2 OBJECTIVE OF THE STUDY Suppose while working as a Geotechnical Engineer, we encounter the following situation: a three-storied office building with load bearing walls has to be constructed. At the site, loosely dumped material exits down to a depth of 7 meters underlain by dense sand. Had the soil at shallow depth strong, such a building could have been founded on strip footings. Three decades ago you would have had to choose between either giving up this site altogether and finding a new site or founding the building on raft or on piles. Both raft and piles are far more expensive than strip footings. Today we have another option, an option that engineers have gradually developed the technology for the last two/three decades, an option that emerged because when engineers encounter such situations they began to ask themselves that “can I make this soil stronger?” and as an answer they develop the techniques to modif y and improve soil. In this study, an effort has been made to use low density polyethylene plastic waste to stabilize the expansive black cotton soil. Black cotton soil procured from gundlupet of Mysore nearby is used. Waste plastic obtained in and around bamboo bazaar industrial area are made available to use as stabilizer. The objective of the study is to understand the effect of plastic waste on the physical properties of black cotton soil rather than the mechanism involved. Few laboratory experiments have been planned to know the quantitative behaviour of black cotton soil stabilized with polyethylene plastic. The term ground improvement and ground modification refers to the improvement or modification to the engineering properties of soil that are carried out at a site where the soil in its natural state does not possess properties that are acceptable to us for the proposed Civil Engineering activity. The following ways of dealing with unsatisfactory soils are available : 1. By pass bad soils 2. Remove bad soils 3. Redesign the structure, and 4. Treatment of soil to improve properties


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A significant increase in bearing capacity may be achieved by altering the soil properties i.e. friction angle, cohesion and unit weight. Various soil improvement methods have been suggested in the past. Some of these method employ the treatment given to soil are at micro levels while some are at macro levels. The objectives of the study are as follows: 1. To study Black Cotton Soil. 2. To study the plastic behavior. 3. To study the behavior of strength gain in the Black Cotton soil.


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CHAPTER 2

LITERATURE REVIEW 2.1 GENERAL Many investigators have conducted the studies on fibre-reinforced materials. The results of direct shear tests performed on sand specimens indicated increased shear strength, increased ductility, and reduced post peak strength loss due to the inclusion of discrete fibres. These results were supported by a number of researchers. Investigations were also conducted to determine the behaviour of material properties of fibre-reinforced sands. The failure envelopes for fibre-sand composites were bilinear. The critical confining stress was a function of surface friction properties of the fibres and soil. The inclusion of discrete fibres increased both the cohesion and angle of internal friction of the specimens. The improvement of the engineering properties due to the inclusion of discrete fibres was determined to be a function of a variety of parameters including fibre type, fibre length, aspect ratios, fibre content, orientation, and soil properties. The peak strength reportedly increased with increasing fibre content and length up to a limiting amount of each beyond which no additional benefits were observed. Cut pieces of HDPE waste milk jugs when mixed with sand have shown that there is an increase in strength, CBR and secant modulus of sand and friction angle increase was as large as 18 degrees. The laboratory study on soils which are mechanically stabilized with short thin plastic strips of different lengths and contents have shown an enhancement of strength and load bearing capacity. Thus it is evident that not much work has been reported on the soil with waste plastic for its application on weak soil like black cotton soil.

2.2BLACK COTTON SOIL 2.2.1 General Black Cotton soils are mainly found over the Deccan lava tract (Deccan Trap) including Karnataka, Maharashtra, Madhya Pradesh, Gujarat and Andhra Pradesh. These soils are found in the river valley of Narmada, Tapi, Godavari and Krishna. These soils have been formed due to the weathering of the lava rocks. This is also known as the Regur soil and Cotton soil. These soils are rich in Iron, Magnesium and Alumina but lack in Phosphorus, Department of Civil Engineering, MIT Mysore

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Nitrogen and Organic matter. It is formed by the weathering of igneous rocks and the cooling of lava after a volcanic eruption. In India, extensive deposits of black soil are found in the Deccan Plateau which includes parts of Karnataka, Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, parts of Tamil Nadu. In the upper parts of Godavari and Krishna, the north western part of Deccan Plateau, black soil is very deep. Expansive soil deposits occur in the arid and semi-arid regions of the world. In India, they have wide development in Bombay, western part of Madhya Pradesh, part of Gujarat, and in some parts of Madras and in Nagpur region. In Bombay, large area is occupied by soils derived from the Deccan trap. In Nagpur region, black cotton soils which are basically an expansive soil are found predominant. Black cotton soils are problematic to the engineering structures because of their tendency to heave during the wet season and shrink during dry season. Different damages in the form of cracking, undulation, differential settlements, etc are experienced by the roads, buildings, irrigation canals, water and sewer lines, etc. Black Cotton soils absorb water heavily, swell, become soft and lose strength. These soils are easily compressible when wet and possesses a tendency to heave during wet condition. Black Cotton soils shrink in volume and develop cracks during summer. They are characterized by extreme hardness and cracks when dry. These properties make them poor foundation soils and earth construction material. The stability and performance of the pavements are greatly influenced by the subgrade and embankment as they serve as foundations for pavements. Roads running in black cotton soils are known for bad condition and unpredictable behaviour for which the nature of the soil contributes to some extent. For developing a good and durable road network in black cotton soil areas, the nature of soils shall be properly understood. On such soils suitable construction practices and sophisticated methods of design need to be adopted. Expansive soil deposits occur in the arid and semi-arid regions of the world. In India, they have wide development in Bombay, western part of Madhya Pradesh, part of Gujarat, and in some parts of Madras and in Nagpur region. In Bombay, large area is occupied by soils derived from the Deccan trap. In Nagpur region, black cotton soils which are basically an expansive soil are found predominant. Black cotton soils are problematic to the engineering structures because of their tendency to heave during the Department of Civil Engineering, MIT Mysore

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wet season and shrink during dry season. Different damages in the form of cracking, undulation, differential settlements, etc are experienced by the roads, buildings, irrigation canals, water and sewer lines, etc. Black Cotton soils absorb water heavily, swell, become soft and lose strength. These soils are easily compressible when wet and possesses a tendency to heave during wet condition. Black Cotton soils shrink in volume and develop cracks during summer. They are characterized by extreme hardness and cracks when dry. These properties make them poor foundation soils and earth construction material. The stability and performance of the pavements are greatly influenced by the subgrade and embankment as they serve as foundations for pavements. Roads running in black cotton soils are known for bad condition and unpredictable behaviour f or which the nature of the soil contributes to some extent. For developing a good and durable road network in black cotton soil areas, the nature of soils shall be properly understood. On such soils suitable construction practices and sophisticated methods of design need to be adopted.

2.2.2 Characteristics of Black Cotton Soil The soil is fine textured and is clayey in nature. It has high qualities of Lime, Iron, Magnesium, and generally poor percentage of phosphorous, nitrogen and organic matter. It is generally Black in colour as it is formed from weathered lava rocks. Soil‟s colour also varies from Black to Chestnut brown. Because of its clayey nature it is highly retentive of water and these soils expand when wet and become difficult to plough. During dry season, black soils shrink and develop big cracks which help in air cir culation. Black Cotton soils are inorganic clays of medium to high compressibility and form a major soil group in India. Black Cotton soil has a high percentage of clay, which is predominantly montmorillonite in structure and black or blackish grey in colour. Because of its high swelling and shrinkage characteristics, the Black Cotton soil has been a challenge to geotechnical and highway engineers. The soil is very hard when dry, but loses its strength completely when in wet condition. The wetting and drying process causes vertical movement in the soil mass which leads to failure of a pavement, in the form of settlement, heavy depression, cracking and unevenness. It also forms clods which cannot be easily pulverized as treatment for its use


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in road construction. This poses serious problems as regards to subsequent performance of the road. Moreover, the softened sub grade has a tendency to heave into the upper layers of the pavement, especially when the sub-base consists of stone soling with lot of voids. Gradual intrusion of wet Black Cotton soil invariably leads to failure of the road. However, since this soil is available easily at low cost, it is frequently used for construction purposes. Some of the factors which influence the behaviour of these expansive soils are initial moisture content, initial dry density, amount and type of clay, Atterberg‟s limits of the soil, and swell potential. Following are the properties of black soil 

Clayey, deep and impermeable

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They swell and become sticky when wet and shrink when dried

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During dry season, these soils develop wide cracks.

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Rich in lime and iron, magnesia and alumina

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They also contain potash

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Lack phosphorus, nitrogen and organic matter

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Colour of the soil ranges from deep black of grey. Hence. It is known as Black Cotton Soil.

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Dark in colour, suitable for cotton cultivation Are residual soils, i.e. they are formed at the place of their origin over the underlying rocks.

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Are formed in situ, i.e. formed where they are found. Therefore, they are essentially formed by weathering of Deccan Trap.

2.2.3 Black Cotton Soil for Cultivation Purpose 

Soil is very fertile in most of the places.

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Poor in nitrogen, phosphorous, potassium, and organic matter and rich in potash and lime.

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Needs irrigation support for cultivation.

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Contains soluble salts in small quantities.

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Cultivation is done with the help of fertilizers.

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Suited for dry farming as it does not require much moisture.

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Cotton cultivation is majorly done.


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Suitable for growing cereals, rice, wheat, jowar, oilseeds, citrus fruits and vegetables, tobacco and sugarcane.

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Their moisture – retentiveness makes them suitable for dry farming.

2.3 SOIL STABILIZERS 2.3.1 General The material in lower layers of pavement structure can be made up of with or without admixtures to increase the load bearing capacity and resistance to physical and chemical factors. The sub-grade of a flexible pavement must have sufficient stiffness and strength and different stabilization techniques can also be used to achieve this. If stabilizers are used to stabilize the sub-grade layer it will prove beneficial and the benefits will be in terms of reduced thickness of sub-grade layer and sub-base layer by reducing the overall cost of construction by some amount.

2.3.2 Uses of Soil Stabilizer 

The most common improvements achieved through stabilization include better soil gradation, reduction of plasticity index or swelling potential, and increases in durability and strength.

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In wet weather, stabilization may also be used to provide a working platform for construction operations. These types of soil quality improvement are referred to as soil modification.

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The strength and stiffness of a soil layer can be improved through the use of additives to permit a reduction in design thickness of the stabilized material compared with an unstabilized or unbound material.

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To control dust and to reduce frost susceptibility.

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Although stabilization can be used to improve foundation layers supporting a paved road thereby reducing the required structural thickness.

2.4 PLASTIC AS SOIL STABILZER 2.4.1 General Plastic is the general common term for a wide range of synthetic or semi synthetic organic amorphous solid materials suitable for the manufacture of industrial products.


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Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs. The word Plastic derives from the Greek (plastikos), “fit for moulding”, from (plastos) “moulded”. It refers to their malleability or plasticity during manufacture that allows them to be cast, pressed, or extruded into an enormous variety of shapes – such as films, fibres, plates, tubes, bottles, boxes, and much more.

2.4.2 Plastic Pollution Plastic is one of the major toxic pollutants of our time. Being composed of toxic chemicals and most importantly a non biodegradable substance, plastic pollutes earth and leads to air pollution and water pollution. There is no safe way to dispose plastic waste. Plastic causes serious damage to environment during its production process and during its disposal process. So the only way to reduce the hazards of plastic pollution is to reduce the use of plastic and thereby force a reduction in its production. The major chemicals that go into the making of plastic are highly toxic and pose serious threat to living beings of all species on earth. Some of the constituents of plastic such as benzene and vinyl chloride are proved to cause cancer, and other gases and liquid hydrocarbons spoil earth and air. The noxious substances emitted during the production of plastic are synthetic chemicals like ethylene oxide, benzene and Xylenes. Besides hitting hard the ecosystem which is already fragile, these chemicals can cause an array of maladies ranging from birth defects to cancer, damage the nervous system and the immune system and also adversely affect the blood and the kidneys. And, many of these toxic substances are emitted during recycling of plastic too. Like in the case of all other chemical substances, „disposal‟ of plastic is a myth. Once plastic is produced, the harm introduced is almost permanent. Plastic defies any kind of attempt at disposal, be it through recycling, burning or land filling. When you recycle a hazard, you pave way for another hazard. Recycling of a plastic merely puts it back into the market place and eventually into the environment, thereby making no reduction in its use. The recycled plastic degrades in quality and necessitates the production of more new plastic to make the original product.


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When plastic is burned, it has its own disadvantages.

When burned, plastic

releases a host of poisonous chemicals including dioxin into the air. Apart from these dangers, recycling of plastic is very uneconomical, dirty and labour intensive as has been revealed by studies conducted by many 'Public Interest Research Groups'. Recycling of plastic is associated with skin and respiratory problems resulting from exposure to and inhalation of toxic fumes, especially hydrocarbons and residues released during the process. Plastic wastes clog the drains and thus hit especially urban sewage systems. The plastic wastes being dumped into rivers, streams and sea contaminate the water, soil, marine life and also the air we breathe. Choked drains provide excellent breeding grounds for mosquitoes besides causing flooding during the monsoon. Since plastic does not undergo bacterial decomposition, land filling using plastic would mean preserving the poison forever. Any attempt to get rid of plastic through landfills is also dangerous. Apart from toxic seepage from the landfill resulting in the contamination of precious water sources, the waste mass impedes the flow of ground water. Landfills are also prone to leaks. The wastes, especially cadmium and lead in the wastes, invariably mix with rain water, then seep through the ground and drain into nearby streams and lakes and other water bodies. Thus the water we use gets poisoned. Plastic is one of the few new chemical materials which pose environmental problem. Polyethylene, polyvinyl chloride, polystyrene is la rgely used in the manufacture of plastics.20% of solid municipal wastes in India are plastic. Non-degradable plastics accumulate at the rate of 25 million tonnes per year. According to an estimate more than 100 million tonnes of plastic is produced every year all over the world. In India use of plastic is 3 kg per person per year.

2.4.3 Plastic Problems Plastics are used because they are easy and cheap to make and they can last a long time. Urbanisation has added to the plastic pollution in concentrated form in cities. Plastic does not decompose, and requires high energy ultra-violet light to break down. Plastic thrown on land can enter into drainage lines and chokes them resulting into floods in local areas in cities as experienced in Mumbai, India in 1998. It was claimed in one of the


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programmes on TV Channel that eating plastic bags results in death of 100 cattle‟s per day in U.P. in India. In stomach of one dead cow, as much as 35 kg of plastic was found. More than 90% of the articles found on the sea beaches contained plastic. The plastic rubbish found on beaches near urban areas tends to originate from use on land, such as packaging material used to wrap around other goods. On remote beaches the rubbish tends to have come from ships, such as fishing equipment used in the fishing industry.

2.4.4 Health Hazards of Plastic A chemical found in plastics used in water bottles, food cans and even dental fillings, could pose a serious threat to the user‟s health, researchers claim. Research on lab animals has linked the chemical to prostate enlargement, declined testosterone, precancerous breast cells, prostate cancer, changes to the genital tract, early puberty in females and hyperactivity. It also acts as an endocrine disruptor meaning it can interfere with the hormone system.

2.4.5 Precautions Ideally, the best methods of reuse are ways that will keep these plastics out of the landfill the longest. Plastic water and soft drink bottles are sold with the intention of single use, then recycling, they can be safely reused if cleaned and handled properly. The keys are to ensure that the bottle is not damaged, has been thoroughly cleaned before each use, and is filled with clean tap water. Different ways to reuse the plastic bags: 

Use them to dust off out-of-season on shoes or seasonal articles.



Use the bags as gloves to clean dustbins, or using pestici des.



When packing a suitcase, use them to keep shoes from soiling clothes and dirty things from clean ones.



To protect small outdoor plants from rain or frost at night, cover them with bags and tie the handles tightly around the pots. Be sure to take the bags off in the morning.


19



Use as a barrier between you and your trash: for those with infrequent trash pickups, use as an extra layer for strong smelling kitchen waste. Or replace trash bags: use for the bathroom, the car, or even to replace kitchen trash bags.



Use as over dirty shoes to avoid tracking mud, or to put over shoes while doing gardening.



Ask stores if they will take the bags back. Encourage your local retailer to do the same.



For those who are interested in something a little bit more long lasting, consider learning how to craft with plastic bags, like carpet, shopping bags.

The only way to overcome the deadly and lasting danger of plastic pollution is to cut down the use of plastic, if possible avoid it altogether. Say NO to plastic whenever and wherever you can. Prefer to

carry your own bags for grocery shopping, a jute or cloth

bag. All attempts made to put an end to plastic pollution will be a REAL BENEFIT for your grand children. Let us contribute our part, save our environment from plastic pollution and make it a better environment for future.

2.4.6 Low Density Polyethylene Plastic as Stabilizer Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various moulded laboratory equipment. Its most common use is in plastic bags.

2.4.7 Properties of LDPE LDPE is defined by a density range of 0.910 – 0.940 g/cm 3. It is not reactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. It can withstand temperatures of 80 °C continuously and 95 °C for a short time. Made in translucent or opaque variations, it is quite flexible, and tough but breakable. LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, since its molecules are less tightly packed and less crystalline because of the side branches, its density is lower. LDPE contains the chemical elements carbon and hydrogen.


20

2.5 STUDIES ON BLACK COTTON SOIL AND PLASTICS Research Article “Industrial Wastes in Soil Improvement” by G. V. Rama Subbarao, D. Siddartha, T.Muralikrishna, K. S. Sailaja, and T. Sowmya, Department of Civil

Engineering, S.R.K. Institute of Technology, Enikepadu, Vijayawada 521108, Andhra Pradesh, India. They presented a study by making an attempt to enhance the geotechnical properties of a soil replaced with industrial wastes having pozzolanic value like rice husk ash(RHA) and fly ash (FA). Soil was replaced with RHA in 2%, 4%, and 6% to dry weight of soil. It was observed that soil replaced with 4% RHA was found to be optimum for the soil used in their study from geotechnical point of view. To know the influence of fly ash, soil was further replaced with 4%FA along with 4% RHA. It was found that the results of soil replacement by both RHA and FA proved to be soil modification and not the improvement. Hence, a cost-effective accelerator like lime was used for further replacing the above soil by 4%RHA-4% FA mix. The optimum lime content was found to be 4%. Anas Ashraf, Arya Sunil, J. Dhanya, Mariamma Joseph, Meera Varghese,M. Veena, B. Tech final year students, College of Engineering Trivandrum, and Mariamma Joseph , Professor, College of Engineering, Trivandrum presented a paper on “ Soil Stabilization using raw plastic bottles”.

Their project involved the detailed study on the possible use of waste plastic bottles for soil stabilization. The analysis was done by conducting plate load tests on soil reinforced with layers of plastic bottles filled with sand and bottles cut to halves placed at middle and one-third positions of tank. The comparison of test results showed that cut bottles placed at middle position were the most efficient in increasing strength of soil. The optimum percentage of plastic strips in soil was found out by California Bearing Ratio Test and using this percentage of plastic, plate load test was also performed. The size and content of strips of waste plastic bottles have significant effect on the enhancement of strength of the soil. “Stabilization of Soil by Using Plastic Wastes” is an international journal paper by Megnath Neopaney, Ugyen, Kezang Wangchuk, Sherub Tenzin, Students of Department of Civil Engineering, and K.Shyam Chamberlin, Assistant Professor, Dept of Civil Engineering, KL University, Vijayawada, AP, India. In this paper, plastic such as shopping bags is used to as a reinforcement to perform the CBR studies while mixing with soil for improving engineering performance Department of Civil Engineering, MIT Mysore

21

of sub grade soil. Plastic strips obtained from waste plastic were mixed randomly with the soil. A series of California Bearing Ratio (CBR) tests were carried out on randomly reinforced soil by varying percentage of plastic strips with different lengths and proportions. Results of CBR tests demonstrated that inclusion of waste plastic strips in soil with appropriate amounts improved strength and deformation behavior of sub grade soils substantially. The proposed technique can be used to advantage in embankment/road construction, industrial yards etc. ”Study on use of plastic waste in road construction” is a paper presented by Mercy Joseph Poweth, Solly George, Jessy Paul , Professors of Department of Civil

Engineering ,M.A .College of Engineering, Kothamangalam, India. They discussed the suitability of plastic waste materials for pavement construction. The waste is mixed in different proportions to the soil sample and their influences on geotechnical properties were studied. The results of the tests indicated that plastic alone is not suitable for pavement subgrade. When quarry dust was added along with soil plastic mix, it maintains the CBR value within the required range. “Use of Waste Plastic and Waste Rubber Tyres in Flexible Highway Pavements” , a paper presented by Rokade.S. of Department of Civil Engineering,

Maulana Azad National Institute of Technology (MANIT), Bhopal 462051, India In this paper, an attempt had been made to use waste plastic, Low Density Polyethylene (LDPE) and Crumb Rubber, blended using dry process for LDPE and wet process for CRMB. Marshal method of bituminous mix design was carried out for varying percentages of LDPE and Crumb Rubber to determine the different mix design characteristics.


22

CHAPTER 3

MATERIALS AND METHODOLOGY 3.1 GENERAL Soil is one of the most important engineering materials. Determination of soil conditions is the most important first phase of work for every type of civil engineering facility. Soil properties are determined by both field and laboratory test methods. In this chapter, we will discuss the several laboratory tests that are performed to determine different properties of soils. These properties are essential for the design of foundation and earth structures.

3.2 MATERIALS FOR STUDY The following are the materials used for our study.

3.2.1 Black Cotton Soil A black cotton soil procured from Gundlupet is used as representative soil in the present study. This soil was collected from an open excavation, at a depth of 1m to 1.5m below the natural ground surface. The Soil used in this study is a blackish gray inorganic clayey soil of medium plasticity. Sufficient quality of soil was brought to the Geotechnical Engineering Laboratory of MIT Mysore. Soil was hand sorted to remove the vegetative matters and organic materials. It was air dried and sieved through 4.75mm and 425 microns IS sieves and stored in tin containers ready for use.

3.2.2 Tests Conducted on Black Cotton Soil The purpose of this investigation is to study the physical and engineering properties of the plain black cotton soil and black cotton soil stabilized with low density polyethylene plastic. The following tests were conducted on black cotton soil: 1. Grain size analysis. 2. Specific Gravity test. 3. Atterberg‟s Limits 

Liquid Limit.



Plastic Limit.

4. Standard Proctor Compaction test. 5. California Bearing Ratio test (CBR test). 6. Unconfined Compression test (UCC test). Department of Civil Engineering, MIT Mysore

23

Grain Size Analysis

The grain size distribution of the soil was ca rried out as per IS: 2720-Part 4, 1985, by wet sieving 300g of soil using 75μm sieve. The portion retained on 75μm sieve was oven dried and sieved using sieves of 4.75 mm, 1.18 mm, 600 μm, 425μm, 300 μm, 150 μm and 75μm sizes. The portion passing 75μm sieve was collected in a tra y and allowed to sediment. The clear water was decanted and the slurry allowed for drying. The particle size distribution analysis was per formed by the sedimentation technique using the hydrometer method. Classification of soils were done using plasticity chart.

Specific Gravity

The specific gravity test was conducted as per IS: 2720 (Part 3/sec-I)-1980 for black cotton soil. The value of specific gravity for BC soil was found to be 2.7

Liquid Limit

The Liquid Limit for all the samples were obtained by using Casagrande's device IS: 2720 (Part-5) – 1985.

Plastic Limit

The plastic limit of the various samples was determined by standard method (test for determination of plastic limit of soil IS: 2720 (part-5) 1985. The plastic limit reported is an average of two determinations.

Standard Proctor Compaction Test

The Standard Proctor Compaction tests can be done to assess the amount of compaction and the water content required in the field. The water content at which the maximum dry density is attained is obtained from the relationships provided by the tests as per IS specifications. Procedure: 



The empty mould was weighed with the base, but without the collar accurately 3kg treated BC soil (BC + varying percentage of plastic) was taken and thoroughly mixed air dried soil



Knowing the natural content, water was added as much as required to make the water content about 6% to 10%, and mixed thoroughly


24



The collar was placed, and the mould was filled with this mix for about half (more than 1/3rd) height and smoothen the surface by gentle pressing.



The mould filled with soil along with collar was mounted on the auto compactor.



The moist BC treated soil was compacted in 3 layers by the rammer of wt 4.89 kg and free fall 45cm with 25 no. of evenly distribution blows to each layer for1000cc mould compactive energy 2700 kJ/m 3



The soil surface was scratched with spatula before placing succeeding layer



The collar was removed and the excess soil was trimmed off.



All the loose soil on the outside of the mould was removed and the weight of the mould with the base plate and soil was taken.



The representative sample was kept for water content.



For treated soil, the above procedure remains same except that the soil was mixed with 4%, 8%, 12% and 16% plastic.

California Bearing Ratio (CBR) Test

The CBR value of a soil is an index which is related to the strength of the soil. The test was conducted in accordance with IS 2720 (Part 16)-1987 The CBR specimen were prepared with different percentages plastic (0%, 4%, 8%, 12% and 16%) as per IS specifications. Standard proctor compaction method was adopted with the help of Auto compactor. A water content of 1%+OMC was added for preparation of specimen. This was to make good the loss of water during mixing. .CBR specimens were casted and soaked in water for 4 days and the test was conducted after soaking the specimen. This was considered as soaked CBR test in the case of soil specimens with plastic. Procedure: 

5 kg treated BC soil (BC + varying percentage of plastic) was taken and thoroughly mixed air dried soil.



Knowing the OMC, water was added to it and was mixed thoroughly with the treated BC soil.



The mould filled with soil along with collar was mounted on the auto compactor.



The moist BC treated soil was compacted in 5 layers by the rammer of wt 4.89 kg and free fall 45cm with 56 no. of evenly distribution blows to each layer for1000cc mould compactive energy 2700 kJ/m 3



The soil surface was scratched with spatula before placing succeeding layer.


25



The collar was removed and the excess soil was trimmed off.



All the loose soil on the outside of the mould was removed.



The specimens prepared were tested for 4 days (soaked).



The specimens prepared were tested at the rate of penetration of 1.25 mm/minute.



A graph of penetration v/s load was plotted and CBR value at 2.5 mm and 5 mm was calculated.

Unconfined Compression Test

The unconfined compressive strength was used to evaluate potential increases in strength for BC soil treated with plastic, compared to untreated samples. The unconfined compression test was used to determine the percentage of plastic in the soil-plastic mixture that would yield the greatest strength increase. The objective of the unconfined compression test is to determine the unconsolidated untrained strength of a cohesive soil in an expensive manner. Specimens are loaded in compression. Load and deflections are measured. The unconfined test uses axial loading without lateral confining pressures, making it the simplest and easiest laboratory method of estimating strength. The UCC test is used to measure the shearing resistance of cohesive soils which may be undisturbed or remoulded specimens. Sample preparation for treated soil :

Specimens of soil and soil stabilized with plastic were prepared by mixing the desired proportions of water (OMC), soil and plastic. Percentages of plastic ranged from 0% to 20% by weight. Specimens were prepared by mixing the BC soil with plastic at 0%,4%,8%,12% and 16% and water added to it was optimum moisture content obtained from Standard Proctor Compaction method. The mixture was compacted in a cylindrical mould, 38 mm in diameter and 76 mm by miniature compaction method. The samples were prepared by miniature compaction method to achieve maximum dry density at optimum water content. The mould consists of steel device with an internal diameter of 38mm and height of 76mm. The volume of steel tube was calculated as equal to the volume of the sample, knowing the volume and the density required. The weight of the sample of trial mixes


26

whose combination percentages were chosen and the water content corresponding to the optimum moisture content was added. This was transferred to the steel-tubing device. It was then compressed by compacting the mixture f from both the top in 5 layers and trimming off the excess soil, samples were then extracted using the sample extruder which resulted in a sample of 38mm diameter and 76 mm height. Test Procedure:

The test was conducted using unconfined compression test apparatus at a strain rate of 1.2mm/min. The specimen to be tested was placed centrally in between the lower and upper platform of the testing machine. The proving ring readings were noted for each 10 divisions on a deformation dial gauge. The loading was continued until three or more consecutive reading of the load dial showed a decreasing or a constant load or a strain of 20% has been reached. The axial stress was plotted against strain and the peak stress was noted. Young‟s Modulus and Unconfined compressive strength was calculated from the graph.

Table.3.1 Properties of Low Density Polyethylene Plastic


27

CHAPTER 4

EXPERIMENTAL RESULTS 4.1 GENERAL This section presents the basic geotechnical properties of Black Cotton soil, compaction characteristics determined for the soils used in the experimental work (untreated and treated), effect of LDPE plastic on stress-strain characteristics of Black cotton soil, effect of LDPE plastic on Unconfined Compressive Strength of Black Cotton soil and effect of LDPE plastic on CBR value of Black Cotton soil. Table 4.1 Geotechnical Properties of Black Cotton Soil

Sl. No.

Properties

Result

Relevant

IS

Code

Gravel-8% 1

Grain Size Distribution

Sand-20%

IS 2720 Part 4

Silt and Clay-72% 2

Specific Gravity (G)

2.7

IS 2720 Part 3

3

Water Content (Natural) (w)

8.668%

IS 2720 Part 2

4

Liquid Limit (WL)

71%

IS 2720 Part 5

5

Plastic Limit (WP)

35.98%

IS 2720 Part 5

6

Plasticity index (IP)

35.02%

IS 2720 Part 5

7

Shrinkage Limit (WS)

15%

IS 2720 Part 6

24.45%

IS 2720 Part 8

8

Optimum

Moisture

Content

(O.M.C)

9

Maximum Dry Density (M.D.D.)

13.49 kN/m 3

IS 2720 Part 8

10

California Bearing Ratio (C.B.R.)

2.55%

IS 2720 Part 16

98.02 kN/m 2

IS 2720 Part 10

11

Unconfined Compressive Strength (U.C.S.) at OMC


28

4.2 STANDARD PROCTOR COMPACTION TEST This section presents the compaction characteristics determined for the soils used in the experimental work. The Standard Proctor test was conducted to determine the optimum moisture content (OMC) and maximum dry density (MDD) of BC Soil (with and without addition of Polyethylene plastic stabilizer). Polyethylene plastic stabilizer was added to the black cotton soil at varying percentages of 4%, 8%, 12% and 16%. The results are shown in Table 4.2.

Table 4.2 Variation in OMC and MDD of Black Cotton Soil with varying percentages of Polyethylene Plastic

BC soil

BC soil+4% Plastic

BC soil+8% Plastic

BC soil+12% Plastic

BC soil+16% Plastic

BC soil+18% Plastic

BC soil+20% Plastic

MDD

12.41

12.60

12.85

12.90

13.50

13.23

13.09

OMC

16.50

18.80

20.95

22.84

24.48

25.60

25.24

MDD

11.90

12.24

12.60

13.27

12.85

12.30

12.05

OMC

19.70

20.40

22.25

23.30

24.20

25.10

26.20

MDD

11.20

11.95

12.35

13.06

12.30

11.74

11.54

OMC

17.30

19.07

20.90

22.82

23.80

24.63

25.30

MDD

10.40

11.27

11.97

12.90

11.52

11.06

10.84

OMC

18.60

19.38

20.10

21.86

22.46

23.11

24.40

MDD

10.03

10.86

11.77

12.67

11.91

10.62

10.37

OMC

18.36

19.89

20.43

21.31

22.41

23.26

24.15

MDD

9.67

10.52

11.76

12.39

11.80

11.05

10.70

OMC

18.20

19.33

20.02

20.82

21.32

22.05

23.12

MDD

9.42

10.30

11.40

12.17

11.67

11.09

10.47

OMC

17.86

18.93

19.65

20.43

21.60

22.12

23.04


29

Table 4.3 Compaction Characteristics of BC Soil (Treated and Untreated)

Materials

Optimum

Maximum Dry

Moisture

Density (KN/m3)

Content (%) BC soil

24.48

13.50

BC soil + 4% Plastic

23.3

13.27


22.82

13.06


21.86

12.91


21.31

12.67


20.82

12.39


20.43

12.17


20.08

12.03

From the table 4.2 and table 4.3, it is observed that Untreated BC soil exhibited Optimum moisture content of 24.48% and Maximum dry density of 13.5 KN/m3. Upon addition of LDPE plastic stabilizer, OMC is decreased from 24.48% to attain the value of 20.43% with 20%stabilizer. However MDD value was found to decrease from 13.5 KN/m3 to 12.17 KN/m3 when 20% stabilizer was added.

4.3 UNCONFINED COMPRESSIVE STRENGTH TEST Specimens of soil and soil stabilized with LDPE5plastic were prepared by mixing the desired proportions of water (OMC), soil and Percentages of LDPE plastic ranged from 0% to 20% by dry weight. Specimens were prepared by mixing the BC soil with LDPE plastic at 0%, 4%, 8%, 12% and 16% with water content equal to respective Optimum Moisture Content obtained from Standard Proctor Compaction method. The mixture was compacted in a cylindrical mould 38 mm in diameter and 76 mm by miniature compaction method. The results of the UCC test are shown as stress v/s strain in the Table 4.4 and Table 4.5. The experimental values for different trials are shown in table below.


30

Table.4.4 Stress-Strain Relation of BC Soil at Different Dosages of Plastic BC soil

BC soil + 4% plastic



Stress

strain

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

34.18

0.67

35.97

0.67

37.77

0.67

41.37

0.67

64.32

1.33

73.25

1.33

78.61

1.33

83.08

1.33

76.31

2.00

102.92

2.00

111.80

2.00

108.25

2.00

82.84

2.67

110.16

2.67

123.37

2.67

126.90

2.67

87.52

3.33

125.15

3.33

141.78

3.33

140.03

3.33

92.13

4.00

129.51

4.00

147.76

4.00

146.02

4.00

94.94

4.67

134.65

4.67

152.78

4.67

148.46

4.67

96.85

5.33

137.14

5.33

155.99

5.33

153.42

5.33

97.02

6.00

156.60

6.00

156.60

6.00

160.56

6.67

166.12

7.33

171.59

8.00


BC soil + 18 plastic


0.00

0.00

0.00

0.00

0.00

0.00

37.77

0.67

39.57

0.67

30.58

0.67

78.61

1.33

80.40

1.33

44.67

1.33

111.80

2.00

104.70

2.00

70.98

2.00

126.90

2.67

116.32

2.67

85.48

2.67

136.53

3.33

114.65

3.33

94.52

3.33

141.67

4.00

126.03

4.00

100.82

4.00

145.87

4.67

129.47

4.67

110.48

4.67

149.14

5.33

131.14

5.33

117.42

5.33

152.34

6.00

131.91

6.00

124.26

6.00

157.18

6.67

133.51

6.67

130.98

6.67

161.09

7.33

137.59

7.33

169.09

8.00

146.60

8.00

172.83

8.67


31

The results of the UCC test are shown as stress v/s strain in the Table4.4. From the table we can absorb the variation in stress-strain characteristics corresponding to varying percentage of plastic. The different curves shows the stress-strain behaviour for the different percentages of plastic like 0%, 4%, 8% 12% ,16%, 18%, and 20%. The curve with the plastic content of 16% shows the maximum value of stress corresponding to strain. Table 4.5 Unconfined Compressive Strength of Black Cotton Soil with varying Percentages of Polyethylene Plastic Plastic Content

Unconfined compressive strength (KN/m2)

0%

98.02

4%

137.14

8%

156.60

12%

171.59

16%

172.83

18%

146.60

20%

130.98

4.4 CBR TEST CBR test was conducted on both untreated and treated BC soil. BC soil was treated with varying percentages of LDPE plastic. The LDPE plastic added was 4%, 8%, 12%, 16% 18% and 20%. The treated samples were cured for 4 days curing period and CBR test was conducted, as per IS 2720 (Part 16) as explained in chapter 3. It was found CBR value at 2.5 mm penetration is higher than the CBR value at 5 mm penetration. Hence the CBR is taken as penetration at 2.5 mm only. Two trials were conducted and the CBR value of the best among the two is considered. The experimental values for different trials are shown below.


32

Table 4.6 Load-Penetration Relations of CBR Test on Untreated and Treated Black Cotton Soil.

Load (KN) for varying dosage of plastic

Penetration in mm BC

4%

8%

12%

16%

18%

20%

22%

24%

SOIL

0.5

15

20

25

30

30

35

40

35

30

1.0

25

30

35

40

40

45

50

45

40

1.5

30

40

45

50

50

55

60

55

50

2.0

35

45

50

55

60

65

70

65

60

2.5

40

50

55

60

65

70

75

70

65

3.0

45

60

60

70

75

80

85

80

75

4.0

50

65

70

75

80

85

90

85

80

5.0

55

70

75

80

85

90

95

90

85

7.5

65

80

90

95

100

105

110

105

100

10.0

75

90

100

110

115

115

120

115

115

12.5

85

100

110

120

125

125

130

125

125

The Table 4.6 shows the load-penetration behaviour of the soil for the different percentage of plastic content. It is evident that inclusion of waste plastic increases the load bearing capacity of the BC soil with the optimum percentage of plastic content. Different CBR curves with different plastic content like 0%, 4%, 8%,12%,16%,18%,20% and 22%. The value with the 20% dosage of plastic content shows the maximum value. Table 4.7 CBR Values for BC Soil treated with varying dosage of LDPE Plastic % of Plastic

CBR Values

0

2.91

4

3.64

8

4.01

12

4.38

16

4.74

18

5.11

20

5.47

22

5.11

24

4.74


33

The CBR value of the untreated soil corresponding to 2.5mm and 5.0mm penetration were found to be 2.919 % and 2.676 % respectively, which were increased to 3.64% and 3.41% respectively when soil was reinforced with 4% waste plastic. Further increase in CBR value was 4.01% and 3.65% for 8% plastic and CBR values of 4.38% and 3.89% for 12% plastic. Again an increase in CBR value to 4.74% and 4.14% for 16% plastic and CBR values of 5.11% and 4.38% for 18% plastic and finally CBR values of 5.47% and 4.63% for 20% plastic respectively. The maximum value of CBR at 2.5mm & 5mm penetration is 5.47% & 4.63% respectively when 20% waste plastic content was mixed with the soil. It can be referred from the figure 5.5 that the CBR value kept increasing up till 20%, and then a decrease in CBR is noticed at 22%. This reveals that at 20% plastic content give us the maximum bearing strength.


34

CHAPTER 5

RESULTS AND DISCUSSIONS 5.1 GENERAL This section presents the compaction characteristics curves determined for the soils used in the experimental work (untreated and treated), effect of LDPE plastic on stress-strain characteristics of Block cotton soil, effect of LDPE plastic on Unconfined Compressive Strength of BC soil and effect of LDPE plastic on CBR value of BC soil.

5.2 STANDARD PROCTOR COMPACTION TEST MDD 15

14

) 13 3 m / N K ( D12 D M 11

10 0

4

8

12

16

20

24

Plastic content (%)

Fig.5.1 Effect of LDPE Plastic on MDD of Black Cotton Soil

From the fig.5.1, it is observed that predominant increase in dosage of LDPE plastic corresponding decrease in maximum dry density and Untreated BC soil exhibited dry density of 13.5 KN/m3. Upon addition of LDPE plastic stabilizer, MDD value was found to decrease from 13.5 KN/m3 to 12.17 KN/m3 when 20% stabilizer was added. Department of Civil Engineering, MIT Mysore

35

Because of using low density plastic material with varying percentages by weight of soil, the dry density of soil gradually decreases.

OMC 25.0 24.5 24.0 23.5 23.0

) % ( 22.5 C M22.0 O 21.5 21.0 20.5 20.0 0

4

8

12

16

20

Plastic content (%)

Fig.5.2 Effect of LDPE Plastic on OMC of Black Cotton Soil

From the fig.5.2 absorb that predominate increase in dosage of LDPE plastic corresponding decrease in optimum moisture content (OMC) of BC soil. It is observed that Untreated BC soil exhibited Optimum moisture content of 24.48%. Upon addition of LDPE plastic stabilizer, OMC is decreased from 24.48% to attain the value of 20.43% with 20%stabilizer. By adding the plastic with the BC soil, the water voids in the can be replaced by the plastic and soil, it will OMC of the BC soil.


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5.3 UNCONFINED COMPRESSIVE STRENGTH 200 180 0% 160 4%

140 ) 2

8%

m120 / N k ( 100 n i a r t 80 S

12% 16%

60

18%

40

20%

20 0 0

1

2

3

4

5

6

7

8

9

% Stress

Fig.5.3 Effect of LDPE Plastic on Stress-Strain Behaviour of Black Cotton Soil

The results of the UCC test are shown as stress v/s strain in the Fig 5.3. From the figure we can absorb the variation in stress-strain characteristics corresponding to varying percentage of plastic. The different curves shows the stress-strain behaviour for the different percentages of plastic like 0%, 4%, 8% 12% ,16%, 18%, and 20%. The curve with the plastic content of 16% shows the maximum value of stress corresponding to strain.


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Axial stress 180 170 160

) ² 150 m / N140 K ( s s 130 e r t s l a 120 i x A 110 100 90 0

4

8

12

16

20

Plastic content (%)

Fig.5.4 Effect of LDPE Plastic on Unconfined Compressive Strength of Black Cotton Soil

From the fig 5.4 it is observed that Untreated BC soil exhibited Unconfined Compressive Strength of 98.02 kN/m 2. Upon addition of LDPE plastic, Unconfined Compressive Strength is increased from 98.02kN/m 2 to attain the value of 172.83 kN/m 2 with16%stabilizer. From the results obtained maximum Unconfined Compressive Strength at the 16% dosage of LDPE plastic.

5.4 CBR TEST CBR test was conducted on both untreated and treated BC soil. BC soil was treated with varying percentages waste LDPE plastic. The % LDPE plastic added was 4%, 8%, 12%, 16%, 18%, and 20%. The treated samples were cured for 4days curing period and CBR test was conducted, as per IS 2720 (Part 16) as explai ned in chapter 3. It was found CBR value at 2.5 mm penetration is higher than the CBR value at 5 mm penetration. Hence the CBR is taken as penetration at 2.5 mm only.


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140 130 120 110 100 90

) 80 N K ( 70 d a 60 o l

0% 4% 8% 12% 16% 18% 20% 22% 24%

50 40 30 20 10 0

1

2

3

4

5

6

7

8

9

10

11

12

Displacement (mm)

Fig 5.5 CBR Curves for BC Soil Treated with different dosage of LDPE Plastic.

The fig 5.5 shows the load-penetration behaviour of the soil for the different percentage of plastic content. It is evident that inclusion of waste plastic increases the load bearing capacity of the BC soil with the optimum percentage of plastic content. Different CBR curves with different plastic content like 0%, 4%,8%,12%,16%,18%,20% and 22%. The curve with the 20% of plastic dosage shows the maximum value.


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5.5

5.0

) 4.5 % ( e u l a 4.0 V R B C3.5

3.0

2.5 0

4

8

12

16

20

24

Plastic content (%)

Fig 5.6 Effect of LDPE Plastic on The CBR Value of BC Soil Treated With Different Dosage of Plastic Content.

It is evident from these figures that inclusion of waste plastic increased the CBR value appreciably. The CBR value of the untreated soil corresponding to 2.5mm and 5.0mm penetration were found to be 2.919 % and 2.676 % respectively, which were increased to 3.64% and 3.41% respectively when soil was reinforced with 4% waste plastic. On further increase in CBR value to 4.01% and 3.65% for 8% plastic and CBR values of 4.38% and 3.89% for 12% plastic. Again an increase in CBR value to 4.74% and 4.14% for 16% plastic and CBR values of 5.11% and 4.38% for 18% plastic and finally CBR values of 5.47% and 4.63% for 20% plastic are obtained. The maximum value of CBR at 2.5mm & 5mm penetration is 5.47% & 4.63% respectively when 20% waste plastic content was mixed with the soil. It can be referred from the figure 5.5 that the CBR value kept increasing up till 20%, and then a decrease in CBR is noticed at 22%. This reveals that at 20% plastic content give us the maximum bearing strength.


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CHAPTER 6

SUMMARY, CONCLUSIONS AND SCOPE FOR FUTURE WORK On the basis of the results and analysis presented, it can be concluded that soil-waste plastic mixtures improve the bearing capacity of the soil. However it may be noted that the analysis carried out herein is only indicative of the possible improvements as the actual improvement depends on the choice of correct dosage of plasti c content in the soil. The study after several experiments, found following significances in using LDPE as stabilizing agent: From view point of Index properties, replacement of soil with 16% Low Density Polyethylene Plastic (LDPE) is the optimum plastic content. The UCC of the original soil is 97.02 KPa. For the soil replaced with 16% LDPE content, the UCC is increased to 172.83 KPa. Therefore, 16% LDPE is the optimum plastic content. The addition of reclaimed plastic waste material to local soil increases the CBR. The maximum improvement in CBR is obtained while using 20% plastic content. The CBR value for Black Cotton Soil is 2.91%. For 20% of plastic dosage, the CBR value becomes 5.47%. This shows the enormous increase in the strength of soil when the plastic is incorporated. Standard proctor Compaction test was carried out for finding the optimum moisture content of the soil for various percentages of plastic content. Based on the laboratory studies carried out in this work, as the percentage of plastic waste increases, the maximum dry density decreases and also the optimum moisture content of the soil decreases. It shows that the increase in the percentage of Plastic content, the water requirement for the soil is reduced since the plastic content occupies the space of water in the soil. Hence, LDPE have a significant influence on the improvement of strength. This new geomaterial can be used as subbase course for pavements. This mix can also be used as a cushioning material under the expansive soil bed. Sustainable development can be achieved through making waste materials to wealthy materials.


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Based on the present study, the following conclusions were drawn 

From the tests conducted on representative black cotton soil indicates that soil posses higher plastic characteristics, lower maximum dry density with higher optimum moisture content , lower CBR and lower UCS, hence soil is weaker.



Increase in percentage of plastic content leads to decrease in dry density and decrease in optimum moisture content implies increased strength.



Addition of low density plastic increased the CBR from a lower value to a considerably higher value.



There is a substantial increase in unconfined compressive strength of black cotton soil treated with plastic.



Low density polyethylene waste plastics can be effectively used to stabilise black cotton soil of this kind.

Scope of Further Study 

Studies can be taken up for other types of soils.



Cost analysis may be carried out for used stabilizer in pavement design.



Field studies can be done.



Studies can be further continued with Low Density Polyethylene plastic in combination with any other stabilizer like fly ash, lime or cement and the results can be compared.


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REFERENCES 1. Khanna S K and Justo C E G, “Highway Engineering”, published by Nem Chand and Bros, 8th Edition 2001. 2. Punmia B C, Ashok Kumar Jain and Arun Kumar Jain, Soil Mechanics and Foundations, Laxmi publications, 2005. 3. IS : 2720 (part-4)- 1985, “Indian standard methods of tests for soils, part -4 Grain size analysis”, published by Bureau of Indian standards, New Delhi 1995. 4. IS : 2720 (part-5) -1985, “Indian standard methods of tests for soils, part -5 determination of liquid limit and plastic limit” , published by Bureau of Indian standards, New Delhi 1995. 5. IS : 2720 (part-9) – 1983, “Indian standard methods of tests for soils, part-9 determination of Dry density and Moisture content”, published by Bureau of Indian standards, New Delhi 1997. 6. IS : 2720 (part-2) – 1973, “Indian standard methods of tests for soils, part-2 determination of water content”, published by Bureau of Indian standards, New Delhi 1997. 7. IS : 2720 (part-10) – 1991, “Indian standard methods of tests for soils, part-10 determination of Unconfined compressive strength”, published by Bureau of Indian standards, New Delhi 1995. 8. IS : 2720 (part-16) – 1987, “Indian standard methods of tests for soils, part-16 laboratory determination of CBR”, published by Bureau of Indian standards, New Delhi 1997. 9. IS : 2720 (part-3) – 1980, “Indian standard methods of tests for soils, part-3 determination of specific gravity”, published by Bureau of Indian standards, New Delhi 1997. 10. IS : 2720 (part-16) – 1987, “Indian standard methods of tests for soils, part-10 laboratory determination of CBR”, published by Bureau of Indian standards, New Delhi 1997. 11. Anas Ashraf et al (2011), Soil Stabilization using raw plastic bottles, Proceedings of Indian Geotechnical Conference, Kochi (Paper No. H-304), pp 1-4. 12. G. V. Rama Subbarao et al (2011), Industrial Wastes in Soil Improvement, International Scholarly Research Network, vol., 2011, pp 1-5.


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stabilization of black cotton soil

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